This invention relates to the manufacture of structural elements from synthetic polymers. More particularly, the invention relates to polyurethane foams reinforced with polyvinyl chloride particles to produce molded shapes which simulate many of the structural properties of wood.
Foamed polymeric materials are produced from a variety of thermoplastic and thermosetting resins by expansion of the polymeric composition during molding, or polymerization in the presence of a blowing agent. Density control is achieved by varying the quantity and type of blowing agent. Rigid and flexible foams of various densities are known and widely available. They are used, for example, for cushioning, thermal and electrical insulation, and structural applications.
Polyurethane foams are produced by condensation of a multifunctional isocyanate and a hydroxyl-containing material, i.e., a polyol. Typically, a polyether or polyester based polyol is reacted with a polyisocyanate in the presence of a catalyst and a blowing agent such as water. The resulting foam may have a density from 0.5 to 50 pounds per cubic foot, (approximately 8 to 800 kilograms per cubic meter), and very low thermal conductivity. These properties, in conjunction with the ready availability and relative low cost of the reactants, make polyurethane foams ideal for use in soft furniture, insulation, automotive and construction components, cushioning, and in other settings.
Polyvinyl chloride is produced by Polymerizing vinyl chloride by suspension, emulsion, or solution methods. It is often copolymerized with up to 50% other compatible monomers. PVC is processed by several methods including blow molding, extrusion, calendering, and coating. Plastisols comprising PVC resin particles dispersed in a liquid phase of a PVC plasticizer are used to produce coatings and molded products. PVC is resistant to weathering, moisture, most acids, fats, petroleum hydrocarbons and fungi. It is dimensionally stable, and has good dielectric properties. It is used for piping and conduits, containers, liners, and flooring.
U.S. Pat. Nos. 2,898,312 and 3,644,229 exemplify compositions and methods for producing polyvinyl chloride/polyurethane hybrid foams. The compositions comprise a polyvinyl chloride resin dispersed in a plasticizer (plastisol), water, a polyol, and a polyisocyanate. The method disclosed in these patents comprises blending a major amount of a polyvinyl chloride plastisol with a minor amount of a polyol, mixing the resulting mixture with a polyisocyanate, and then placing the three part mixture in a suitable mold. The disclosed compositions and methods are said to result in a foamed, cellular material. Processing requirements limit the useful polyether polyols to those with molecular weights between about 500 and about 3,000.